The present invention relates to heat exchangers having a core of cooling tubes with a tank at each end of the core and in particular to a heat exchanger in which the core tubes are directly joined to the tank without an intermediate head sheet.
Typical liquid to air heat exchangers, such as automotive radiators, include a core assembly of a plurality of cooling tubes with fins. The cooling tubes extend between spaced head sheets or header plates. The end of the tubes extend through apertures in the head sheets and are sealed thereto, typically by brazing. A tank formed as a three dimensional stamped metal body or a molded plastic body having an open side, is joined to each of the head sheets and sealed thereto to form a closed tank at each end of the core. Fluid flows from one tank through the cooling tubes to the other tank. A second fluid, typically air, passes between the fins to remove heat from the cooling tubes and thereby cool the fluid in the tubes as it flows from one tank to the other.
The seal between each tank and the head sheet is difficult to properly from and can be the source of leaks during the use of the heat exchanger. Accordingly, it is an object of the invention to provide an improved heat exchanger construction that overcomes the problems associated with the sealing of the core head sheet to the tank.
The present invention overcomes the problems in the prior art by forming the tank and head sheet as an integral, single piece body. A closed tank is formed with apertures along one side for receiving the cooling tubes. The tubes are then inserted directly into the tank. This eliminates the need for a separate head sheet and the need to seal the separate head sheet to the tank. The tubes are sealed to the tank by brazing, in a conventional manner, for constructing a heat exchanger.
The heat exchanger tanks are shaped by a hydroforming process in which an elongated tubular blank is first placed in a die cavity that matches the tank s desired shape. The interior of the tubular blank is sealed and then highly pressurized with a fluid, such as water or oil, so that its outer surface is forced to take the shape of the cavity.
The hydroforming cavity includes inwardly projecting chisel points or punches. After the tube assumes the cavity shape the punches are actuated and pierce the tank.
During hydroforming, outwardly projecting ribs are formed between each of the cooling tube receiving apertures to stiffen the tank. These ribs extend in a circumferential direction relative to the tube longitudinal axis. Cylindrical projections from the tube are also formed during hydroforming. These projections form inlet and outlet necks for the tanks. During hydroforming, the cylindrical projections have closed ends. These ends are later removed, forming the open cylindrically shaped necks.
The open end or ends of the tube blank are closed with an end cap after the tank is hydroformed. The end caps are sealed to the tank by brazing.
An auxiliary oil cooler can be disposed in one of the tanks. The inlet and outlet tubes of the auxiliary cooler extend through one of the tank end caps. The end cap at the opposite end of the tank can be shaped to form a support ledge for supporting the end of the auxiliary cooler. The fluid in the oil cooler is cooled by the first fluid which is typically water or a mixture of anti-freeze and water. Alternatively, the auxiliary oil cooler can be attached to one of the tanks and the other of the tanks to provide structural support thereto and to permit the auxiliary oil cooler to be cooled by a second fluid, such as air.
During hydroforming, outwardly or inwardly extending protrusions can also be formed on the tank to locate the heat exchanger on a rubber mount when attaching the heat exchanger to a supporting structure. The protrusion is typically disposed into a groove in the rubber mount. The rubber mount isolates the heat exchanger from vibration of the support structure, such as an automobile.
Further objects, features and advantages of the invention will become apparent from a consideration of the following description and the appended claims when taken in connection with the accompanying drawings.